1. Field of the Invention
The present invention relates to an optical semiconductor device used in a transmitter for use in optical fiber communication and to a method of manufacturing the optical semiconductor device.
2. Background Art
Optical modulator integrated semiconductor laser devices having a semiconductor laser part and an optical modulator part integrated on a semiconductor substrate are used (see, for example, Japanese Patent Laid-Open No. 2009-295879). In ordinary cases, the optical modulator part and the semiconductor laser part are of a vertical ridge type (see, for example, Japanese Patent Laid-Open No. 2002-131713). In the vertical-ridge-type optical modulator part, however, the device resistance is increased in proportion to the area of the ridge top and the frequency characteristic deteriorates correspondingly. For this reason, the vertical-ridge-type optical modulator part is not suitable for high-speed modulation at 25 GHz or higher, for example. A construction having both the optical modulator part and the semiconductor laser part provided in inverted-mesa ridge form to reduce the device resistance of the optical modulator part has been proposed (see, for example, Japanese Patent Laid-Open No. 2002-204030).